Abstract
Resonance Raman (RR) spectra of the "rapid" and "slow" forms (Baker et al., 1987) of resting cytochrome oxidase obtained with Soret excitation at 413.1 nm are reported. There are a number of conspicuous differences between the two forms in the high-frequency region of the RR spectrum which involve changes in Raman intensity arising from a blue shift in the Soret maximum of cytochrome a3 upon conversion to the slow form. In the low-frequency region a peak present at 223 cm-1 in the rapid form shifts to 220 cm-1 in the slow form; this peak is assigned as the cytochrome a3 Fe(III)-N(His-Im) stretch. The slow form of the enzyme possesses greater intensity in RR peaks near 1620 cm-1 which have been previously attributed by others to partial photoreduction of the enzyme. We have quantitated the amount of laser-induced photoreduction in these RR spectra by comparison with the spectra of mixed-valence derivatives of the enzyme and find that these 1620-cm-1 features are unreliable indicators of photoreduction. The spectra of the fast- and slow-reacting species in H2O and D2O have been compared. The fast-reacting form exhibits a 4-cm-1 shift, from 223 to 219 cm-1, upon transferring to D2O in a peak which we assign as the cytochrome a3 Fe(III)-N(His-Im) stretch. There is a parallel shift in the feature at 1651 cm-1 due to the C = O stretch of the formyl group of cytochrome a. These deuterium shifts are not observed in the slow form.(ABSTRACT TRUNCATED AT 250 WORDS)
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